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 9 Three Idols Here's a classic: Three gods A, B, and C are called, in some order, True, False, and Random. True always speaks truly, False always speaks falsely, but whether Random speaks truly or falsely is a comp ... Submitted by Aakash Hard 9.1 8 Attic Lamp Switch A downstairs panel contains three on-off switches. One of them controls the lamp in your attic. Using only ONE trip up to the attic, how do you determine which switch controls the lamp? Submitted by Valentin Doable 5.3 12 Choose the Next Letter Choose the next letter in the sequence: O T T F F S S ? Submitted by Ravi Doable 4.0 7 Cooking Time A cook must put a souffle exactly 9 minutes at the oven, but he only have a 7 minutes hourglass and a 4 minutes hourglass. How can he measure 9 minutes with those clocks? Submitted by Ravi Doable 5.7 28 12 Identical Balls You have 12 identical balls. One of them is slightly different in weight than the rest. You have three weighs of a balance scale to determine which ball is different and whether it is heavier or li ... Submitted by Valentin Doable 6.2 5 The Stealing Mailman This is a fairly simple problem that can cause some people trouble. Kevin and Sophia want to mail high confidential letters between each other. They know that the mailman is crooked and opens the le ... Submitted by Ravi Doable 6.5 7 The Neighbourhood People say Einstein suggested that 98% of the world’s population couldn’t figure out the answer to this puzzle. It is not for the faint of heart: There are 5 houses each with a different color. Th ... Submitted by Aakash Hard 7.5 4 Don't Mate in One This problem was first publicized by Karl Fabel, a German chess problemist. Find a move for white that will not result in an immediate checkmate of the black king. Submitted by Aakash Doable 6.6 11 Measuring Up You have a 3 and a 5 litre water container, each container has no markings except for that which gives you its total volume. You also have a running tap. You must use the containers and the tap in su ... Submitted by Ravi Easy 3.1 4 Time To Fuse You have a string-like fuse that burns in exactly one minute. The fuse is inhomogeneous, and it may burn slowly at first, then quickly, then slowly, and so on. You have a match, and no watch. How do ... Submitted by Valentin Doable 4.5 4 Balloon Business You’re sitting in a stationary car. There’s a helium balloon tied to its floor. You accelerate and, obviously feel like you’re being pushed backwards (against the direction of your acceleration). W ... Submitted by Valentin Doable 4.0 7 Tea and Wine You take a spoon of wine from a barrel of wine and put it into your cup of tea. Then you return a spoon of the (non-uniform) mixture of tea and wine from your cup and put it in the barrel. Now you ha ... Submitted by Ravi Doable 4.7 5 Clock Hands - Google Interview Question How many degrees are there in the angle between the hour and minute hands of a clock when the time is a quarter past three? Submitted by Valentin Doable 3.5 8 Prisoners and hats 100 prisoners are standing in a line each 1 seeing the back of the ones in front of him. Each prisoner is given a black or a white hat. If they can guess the color of their hat they can go away freel ... Submitted by Valentin Hard 8.5 56 All the King's Wine So there's this king. Someone breaks into his wine cellar where he stores 1000 bottles of wine. This person proceeds to poison one of the 1000 bottles, but gets away too quickly for the king's guard ... Submitted by Aakash Hard 7.5